A. Field of Invention
This invention relates to a bi-directional clutch, and, more particularly, to a clutch having internal gears to provide a mechanical advantage. The clutch is particularly useful for operating a window dressing such as a roller shade.
B. Description of the Prior Art
Roller shades are often used as window dressing and provide both a practical and an esthetic function. Typically, a roller shade includes a tubular mandrel and a decorative panel wound on the mandrel. The mandrel can be selectively rotated by a user either in one direction or the other causing the panel to be either raised or lowered, depending on how it is wound on the mandrel. The roller shade is provided at its two ends with mounting means so that it can be mounted on a window frame or other similar location, using suitable brackets. Normally, one end of the roller shade is a simple rotatable coupling that allows the roller shade to rotate with respect to the bracket. The other end is provided with a bi-directional clutch that provides a mechanical advantage during the operation of the roller shade. Bi-directional clutch mechanisms of this type are disclosed in U.S. Pat. Nos. 4,433,765 and 4,372,432, incorporated herein by reference. These reference disclose clutch mechanisms in which the mechanical advantage is developed between a large pulley and a small shaft. One or more springs are also provided as a means for locking the mandrel to prevent undesirable rotation. Other clutch mechanisms are also known which are based on frictional braking. U.S. Pat. Nos. 3,135,369 and 3,920,106 also disclose bi-directional clutches useable for roller shades.
Recently there has been an increased need for roller shades having larger sizes and/or weights which in turn require stronger clutch mechanisms with a larger mechanical advantage, normally requiring more space. However, in the existing roller blinds, since mechanical advantage is dependent on the relative diameters of a pulley and a small shaft, and since the shaft has already been minimized, the mechanical advantage can be increased by increasing the size of the pulley. However, this is not a practical solution because space is too limited to accommodate a larger pulley, and in addition, a larger pulley may not be esthetically unacceptable.
In addition, a stronger clutch mechanism requires more springs for locking the roller blind to prevent its undesirable rotation. However, more springs complicate the structure of the clutch mechanism, and increase the force required to operate the same.
Accordingly, it is a broad objective of the present invention to provide an improved bi-directional clutch particularly suited for roller shades and other window dressings.
It is a further objective to reduce the number of springs required and thereby reduce the inherent friction associated with the operation of the bidirectional multi-spring clutch.
It is still a further objective to locate the gear box between the user interface (for example, a cord or a bead chain) and the wrap springs of the clutch to permit the use of less force in releasing the wrap spring of the clutch to yield a user interface with a smother performance.
Yet another objective is to provide a clutch mechanism that can provide a larger mechanical advantage then previous clutch mechanisms but without a corresponding increase in size.
These and other objectives of the present invention are obtained by providing a clutch, particularly useful for operating a window dressing, that includes an input member arranged to be activated by a user for operating the window dressing; an output member coupled to the window dressing, antirotational means adapted to prevent the output member from rotation in response to a rotational torque from the window dressing, and a gear box coupled to the input member and adapted to transmit a rotational motion at a mechanical advantage to the output member in response to the activation of said input member. The input member may include an elongated element such as a cord, a string, a chain, etc., arranged for pulling by the user. The gear box includes a gear pulley coupled to the elongated member and arranged to rotate in response to the pulling of the elongated element.
The gear box includes a stationary gear, a stationary drum attached to the stationary gear, a rotating member mounted coaxially on the drum and a planetary gear arranged between the gear pulley and the stationary gear to transfer rotation to the rotating member.
The antirotational means is associated with the stationary drum and the rotating member and it includes spring coils adapted to selectively form an interference fit with the stationary drum, thereby preventing undesirable rotation of the rotation member.
In another aspect of the invention, the clutch is provided for operating a window dressing mounted on a stationary structure, and includes an end member adapted for mounting the window dressing to the stationary structure. The end member receives a cord adapted for manipulation by a user to operate the window dressing. The end member includes a gear box adapted to translate a movement of the cord into a rotation at a preselected mechanical advantage. An output member is adapted to couple the rotation to the window dressing. In addition, an antirotational member is coupled to the output member to prevent undesirable rotation.
In another aspect of the invention, a bi-directional clutch is provided for supporting a window dressing on a structure. The clutch includes a protective guard adapted to be secured to the structure. The protective guard is provided with a disk with a lip and a drum disposed coaxially on the disk. A drive is also provided that has a boss and hub. The hub is facing the lip to define a chamber, and the boss is disposed telescopically over said drum. A tubular housing is provided that is disposed telescopically over the boss and is adapted to engage the window dressing. A gear box is disposed in the chamber, and is coupled to an elongated operating member. The gear box is adapted to transfer a rotation to the tubular housing when the elongated operating member is manipulated by the user. Preferably, the clutch includes an antirotational member disposed between the drive and the tubular housing and is adapted to prevent undesirable rotation of the tubular housing. The antirotational member includes a coil spring wound between the drum and the boss.
The gear box includes a gear pulley arranged to receive the elongated member, including internal teeth. A stationary gear is attached to the protective guard and one (preferably several) planetary gear rotationally mounted between the internal teeth and the stationary gear. The planetary gear is mounted on the hub.